Characterization of livestock-associated methicillin-resistant Staphylococcus aureus strains by MALDI-TOF MS technique

Background: The livestock-associated methicillin-resistant Staphylococcus cures (LA-MRSA) infections are growing animal health and economic problem in many parts of the world. In Europe, the strains of CC398 LA-MRSA clonal lineage were identified in pigs for the first time between 2003 and 2005, however have since been isolated from several species. Colonization is usually asymptomatic, however it can cause infections both in human and animals. Objectives: In the present study, strains isolated from animals (horse, swine, cattle) were analysed by MALDI-TOF MS technique. Specific peaks as defined in previous studies were tested on CC398 and CC1 LA-MRSA strains, which were allow determining the methicillin resistance and distinguishing the CC types. Materials and methods: During the examination 12 MRSA strains were analysed, from which 8 strains belonged to the clonal complex 398 and 4 belonged to the clonal complex 1. From the sample-preparation protocols, formic acid suspension method was used with alpha-HCCA matrix. During the identification, 6 technical replicates were performed for each strain. Isolates were identified using MALDI BioTyper 2.0 software, furthermore the specific peaks of antibiotic resistance and CC were analysed in FlexAnalysis software. Result and discussion: Based on the result of best matches and best score values all strains were identified as S. aureus and S. aureus ssp. aureus by MALDI BioTyper. 7 out of 9 antibiotic resistant specific peaks were detected in more than 40% of the strains, however the peaks at 5070 m/z and 9632 m/z appeared in all strains. The peaks at 3037 m/z and 4511 m/z allow to distinguish CC398 and CC1 strains. The MALDI technique is suitable for the identification of MRSA strains and distinguish the tested CC types, thereby it offers new opportunities in veterinary diagnostic and surveillance.